Manviri Rani

Recent strategies for removal and degradation of persistent & toxic organochlorine pesticides using nanoparticles: A review

Organochlorines (OCs) are the most hazardous class of pesticides, therefore, banned or restricted in several countries. The major sources of OCs include food industries, agriculture and sewage wastes. Their effluents discharged into the water bodies contain extremely high concentration of OCs which ultimately causes environmental concern. Because of their high persistence, toxicity and potential to bioaccumulation, their removal from wastewater is imperative. The degradation techniques are now advanced using nanomaterials of various kinds. During the last few years, nanoparticles such as TiO2 and Fe are found to be excellent adsorbents and efficient photocatalysts for degrading more or less whole OCs as well as their toxic metabolites, which opens the opportunities for exploring various other nanoparticles as well. It is noteworthy that such methodologies are economic, fast and very efficient. In this review, the detailed information on different types of OC pesticides, their metabolites, environmental concern and present status on degradation methods using nanoparticles have been reviewed. An attempt has also been made to highlight the research gaps prevailing in the current research area.

Degradation of hazardous organic dyes in water by nanomaterials

There is about 700,000 tonnes of dyes, of more than 10,000 types, that are used as coloring agents in industries, mainly for textile. The release of dyes in natural media is of concern due to their high persistence, toxicity and potential to the bioaccumulate in living organisms. In particular, the most commercialized and carcinogenic azo dyes, that pocess a benzidine function, needs urgent attention. Here, we review the current status of cationic and anionic dyes. We present dye removal techniques using nanoparticles through adsorption and degradation. Among dye removal techniques, adsorption was found the most efficient and cheap. For that, conventional adsorbents such as commercial activated carbon, chitosan and natural waste are often employed. We discuss the use of ZnO, TiO2 and Fe0 to remove dye pollution.

Towards green synthesis of nanoparticles: From bio-assisted sources to benign solvents. A review

ABSTRACT Current advancements in green synthesis of materials especially nanoparticles have led to conservation of natural and non-renewable resources along with reduction in environmental pollution. Development of cost-effective, simple and eco-friendly routes for the synthesis of nanoparticles is very important. All over the world, a wide variety of biogenic sources have been put to trial as a source of green agents to facilitate synthesis process. In addition to this, environmentally benign solvents are also being used these days in order to promote green synthesis. In this review, an attempt has been made to familiarise the readers with the different green routes for the synthesis of nanoparticles.

Catalytic removal of organic colorants from water using some transition metal oxide nanoparticles synthesized under sunlight

Transition metal oxides (TMO) constitute a most amazing class of materials with a wide range of properties and applications; therefore, their synthesis using a green approach is a necessity. As such, sunlight irradiation was employed to synthesize various TMO nanostructures (ZnO, CuO, Co3O4, NiO and Cr2O3) using water as a solvent. Nanoparticles obtained with distinct morphologies, such as nanotubes (ZnO; 86.86% (CuO) > 85.89% (NiO) > 80.35% (Co3O4), depending on the sizes of the respective TMO nanoparticles. This is also supported by the finding of small and non-toxic by-products such as but-2-enal, sulfur trioxide and benzoquinone. With high potential observed in the removal of dyes, TMO nanoparticles have a bright future with respect to their use as important adsorbents in waste water treatment. The advantage of the present work lies in the green synthesis of nanoparticles and their application in helping to make our environment green.

Degradation of traditional and new emerging pesticides in water by nanomaterials: recent trends and future recommendations

Rapid industrialization and extensive use of pesticides in agriculture practices have contributed to the leaking of pesticide residues into water. Among them, organochlorines are highly toxic with half-lives of many years followed by organophosphates (OPs). Being banned in many countries, most of the pesticides are still persisting in the environment. Due to high perseverance, toxicity and potential to bioaccumulation, their removal is imperative. In this direction, conventional adsorbents such as commercial activated carbon, agricultural and natural waste were highly employed. In modern era, nanomaterials (including nanocomposites and nanobiocomposite) with high surface area come out as most economic, rapid and effective catalyst. TiO2 (photocatalyst) and Fe0 by itself or with oxidizing agents are playing a promising role in elimination of pesticide pollution and open the opportunities for exploring other nanoparticles as well. Further, their modified, doped or composites form showed enhanced characteristics due to introduction of new energy levels or increase in surface area. In contrast to TiO2 and Fe0, various nanostructured metal oxides found to degrade OP pesticides by rapid reactive adsorption followed by cleavage of P–O bond via SN2 mechanism. The present review focuses on the present status of pesticide removal using nanoparticles through adsorption together with photocatalytic or redox or reactive degradation. Herein, detailed information on several pesticides, problems related to pesticide, their metabolites, environmental concentration and need for degradation has been presented. In addition, importance of green synthesized nanoparticles along with limitation and potential health risk of nanomaterials in degradation of various organic pollutants has been highlighted.

Remediation of Polycyclic Aromatic Hydrocarbons Using Nanomaterials

Polycyclic aromatic hydrocarbons are major contaminants in environmental bodies due to ubiquitous occurrence, toxicity and potential to bioaccumulation. Increased population, rapid industrialization and extensive use of oil fuels are one of the major cause of pollution by polycyclic aromatic hydrocarbons. Here, we review the issues related to polycyclic aromatic hydrocarbons (PAHs) and their removal techniques using nanoparticles through adsorption, photocatalytic and redox degradation. Among the dye removal techniques, adsorption was found best in terms of its efficiency and economy. For that, traditional techniques such as microbial, photolysis and conventional adsorbents such as commercial activated carbon, agricultural and natural waste are highly employed. Lately, low cost nanomaterials with high surface-area come out as most economic, rapid and effective green adsorbent cum photocatalyst under UV and sun-light irradiation. Green synthesized nanomaterials with advanced characteristics of adsorbent and photocatalysts are gaining importance in degradation of various organic-pollutants due to low cost of production and mediated effect of biogenic sources. We also discuss the use of TiO2, ZnO and metal hexacyanoferrate to remove polycyclic aromatic hydrocarbons pollution.

Insight in to the degradation of bisphenol A by doped ZnO@ZnHCF nanocubes: High photocatalytic performance

Bisphenol-A (BPA) is suspected of been endocrine-disrupter and carcinogen. Hence, removal of extensively used BPA by low-cost and efficient coupled-nanomaterials is viewed as vital to environmental protection. Herein, nanocomposite of ZnO doped with zinc-hexacyanoferrate (ZnO@ZnHCF) was employed for photodegradation of BPA. Green synthesized nanocomposite consisted of ZnO wrapped ZnHCF distorted nanocubes piled together. Under daylight, prompt early exponential decline in concentration over time revealed elevated photo-activity of nanocomposite. Improvement in surface-area (113.491 m2g-1) and band-gap (2.2 eV) of catalyst was resulted from synergism of semiconducting and intercalative feature of ZnO and ZnHCF. At optimum catalyst-dose (25 mg) and neutral pH, photodegradation of BPA (97% of 2 mgL-1) followed first-order-kinetics involving initial Langmuir adsorption isotherms (R2 ≥ 0.996; p ≤ 0.05). Nanocomposites were more effective for greater adsorption of BPA (Xm = 18.0 mg g-1) than the ZnHCF (10.8 mg g-1) and ZnO (3.9 mg g-1). Moreover, doped ZnO@ZnHCF reduced the half-life of BPA upto 2.8 h than that with bared ZnHCF (8 h) and ZnO (17.4 h). GC-MS revealed presence of smaller and safer byproducts clearly supported electron excitement from wrapped-nanocomposite followed by oxidation of BPA with countless OH. Degradation pathways were constructed to track-ways leading to mineralization. Overall, due to greater surface-activity, reusability upto ten-cycles and charge separation (e-+h+ pairs) led to promotion of huge free radicals, ZnO@ZnHCF might be supposed a promising photocatalyst.